Microsoft 365 vs. Azure: Choosing the Right Service for High-Volume Emails

Sarah Lean -

Sending high-volume emails is common for large organisations. They need to reach employees, customers, or both. Some use mailing services like Mailchimp, SendGrid, or MailerLite. Others prefer to handle bulk emails in-house.

If your organisation uses Microsoft 365, recent changes may affect you. Microsoft has introduced new restrictions on high-volume emails to improve security and system stability.

As a result, many businesses are rethinking their email strategy. In this article, I’ll explore two Microsoft solutions for high-volume email:

  • High Volume Email (HVE) – A built-in option within Microsoft 365.
  • Azure Communication Services (ACS) – A cloud-based alternative for large-scale email campaigns.

Let’s dive in.

High Volume Email (HVE) Service

In April 2024 Microsoft introduced the High Volume Email (HVE) service. At the time of writing, it is still in public preview but is expected to become a production service by September 2025. 

The HVE service is designed to allow users to send up to 100,000 INTERNAL emails per day per tenant. 

As well as allowing you to be able to send internal emails, you do have the capability to send external emails but that is limited to 2,000 recipients per date. 

Within your Microsoft 365 tenant, you can create up to 20 HVE accounts, they are mail user accounts, but you should avoid giving any license to your HVE accounts.  You might want to set up different HVE accounts for different use cases, for example, one for emails your Human Resources (HR) department sends out, or maybe accounts related to the regional offices you have. 

It's important to note that HVE is primarily intended for internal communications. For high-volume EXTERNAL email needs, Microsoft recommends using Azure Communication Services (ACS), which is designed to handle large-scale transactional, bulk, and marketing emails to external recipients.

Azure Communication Services (ACS)

Azure Communication Services (ACS) is a multichannel communication API you can use to send voice, video, chat, text messaging/SMS, email and more. 

This is a service that has been generally available since 2021. 

In terms of the email side of things, it is designed to send out large volumes of emails to external recipients.  It does have a limit of only being able to send an email to 50 recipients at a time and also the maximum size of the email, including attachments is 10MB. 

ACS provides REST APIs and SDKs that allow engineers to integrate email functionality into their applications.

You can associate domains with Azure Communication Services (ACS) so you can send emails from known domains that your customers will recognise.

ACS charges per email sent and also per MB transferred.  Each email you send costs $0.00025 and each MB transferred costs $0.00012. 

So if you were to send 1,000 emails, each 1MB in size the total cost would be: $0.25 (emails) + $0.12 (data) = $0.37

Conclusion

Both services have their merits, it’s about understanding your requirements and picking the service that meets your requirements. 

If you're primarily sending internal emails within your organisation, High Volume Email (HVE) in Microsoft 365 is a built-in option. 

For large-scale external email campaigns, Azure Communication Services (ACS) offers a flexible, API-driven approach that allows organisations to send high volumes of emails from recognised domains at a cost-effective rate.

By understanding these differences, you can make an informed decision on which service to use.